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Voltage testing

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Rick

09-19-2000 18:45:57




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When taking voltage readings at the coil, I get an initial reading of a little over 4 volts and then the voltage starts dropping rapidly. I guess the resistors are doing their job? Should the voltage be measured this way or am I missing something? After the initial reading I cannot get the volt readings to read at that level agan until the resistors cool down. Thanks for your info.

Rick 8N 245054

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Bill(NC)

09-20-2000 03:53:12




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 Re: voltage testing in reply to Rick, 09-19-2000 18:45:57  
I think I screwed up and need to re-do this post!

I think I read on this board (and it made sense to me) that the resistor is supposed to have lower resistance to start, thereby applying a higher voltage to the coil. As the resistor heats up, the voltage on the coil should drop to approx 4 Volts. The reason for this is because when starting the engine, the starter motor draws a lot of current and drops the battery voltage. You need more voltage on the coil at that time. If you have 4 Volts on the coil after things settle down, and the tractor starts, you are probably OK.

Bill Malpass

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Bill(NC)

09-20-2000 03:51:01




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 Re: voltage testing in reply to Rick, 09-19-2000 18:45:57  
I think I screwed up and need to re-do this post!

I think I read on this board (and it made sense to me) that the resistor is supposed to have lower resistance to start, thereby applying a higher voltage to the coil. As the resistor heats up, the voltage on the coil should drop to approx 4 Volts. The reason for this is because when starting the engine, the starter motor draws a lot of current and drops the battery voltage. You need more voltage on the coil at that time. If you have 4 Volts on the coil after things settle down, and the tractor starts, you are probably OK.

Bill Malpass

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Dell (WA)

09-19-2000 21:02:29




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 Re: voltage testing in reply to Rick, 09-19-2000 18:45:57  
Rick..... A good voltmeter is "invisable" to the circuit being measured. Something is not right. You are taking the readings on a stopped engine?
If you are taking the readings on a running engine, that tells me your frontmount ignition coil is heating up and the internal coil windings are shorting out. If this is the case, I'd be for replacing the ignition coil because it should not do that.

Good 6 volt frontmount ignition coil should read about 3.5 volts (3 min, 4.5max) with the points closed, battery voltage with the points open. anything else, you're going to have sparky problems..... ...Dell

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Dell (WA)

09-19-2000 21:00:27




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 Re: voltage testing in reply to Rick, 09-19-2000 18:45:57  
Rick..... A good voltmeter is "invisable" to the circuit being measured. Something is not right. You are taking the readings on a stopped engine?
If you are taking the readings on a running engine, that tells me your frontmount ignition coil is heating up and the internal coil windings are shorting out. If this is the case, I'd be for replacing the ignition coil because it should not do that.

Good 6 volt frontmount ignition coil should read about 3.5 volts (3 min, 4.5max) with the points closed, battery voltage with the points open. anything else, you're going to have sparky problems..... ...Dell

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Rick

09-20-2000 05:08:29




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 Re: Re: voltage testing in reply to Dell (WA), 09-19-2000 21:00:27  
Dell, I am taking readings at the coil with the engine NOT running. I indeed have a front mount dist. It has been converted to 12 volts and has an OEM terminal block/ballast resistor and a RU-100 12 to 6 volt reducer wired in series going to the coil. I used the tractor 7hrs. Sat. and 3hrs Sun. and the tractor worked fine. On the way to the last field the tractor seemed to quit running on 2 cylinders(3&4). Would a fried coil produce these symptoms? If so should I replace the 6 volt coil with a 12 volt coil and eliminate the RU-100 reducer? After a re-build I have about 12 hrs on engine. I have replaced all dist. prts. except shaft and condensor, which was put in at rebuild. Thanks for any thoughts.

Rick 8N245054

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Dell (WA)

09-20-2000 06:54:49




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 Re: Re: Re: voltage testing in reply to Rick, 09-20-2000 05:08:29  
Rick..... .yep...bad coil most likely, altho a shorted condenser could also give you the same symptoms. Condensers are cheeper than coils but usually more reliable. You can test your condenser with an "ohm meter", it should kinda go towards zero and then build up toward infinate ohms. For $2, just bite the bullet and replace it if you have any doubt.

As for wheather to change to a 12 volt frontmount coil without the RU-100 12 to 6 volt reducing resistor, your dollar. You still need some sort of a ballast resistor with the 12 volt coil. The coil should come with a recommended value of resistance.

As for your 3&4 miss. I'd check it out at night and watch for blue sparkies running around outside the ignition wiring. Make certain all your sparkplugs are gapped at 0.025, DO NOT expect new sparkplugs out of the box to be gapped correctly.

N.B.....The wider the gap, the more sparkie voltage you need. If your coil is going bad, the sparkies won't jump the gap. I had a mechanics class one time where there was this new big t.v. spark display scope on it. The instructor insisted that all 8 sparkplug voltages be the same amplitude, which was obtained by individually gapping each sparkplug differently. Talk about being time consumming and frustrating. Lesson learned..... ...Dell

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